This invention relates to a self-retaining needle that is pierced into a blood vessel as in the case of transfusion. It also relates to a valve element for use in the needle.
To perform transfusion on a patient, a self-retaining needle to be connected to a transfusion line is pierced into a blood vessel of the patient and held in position. The self-retaining needle consists of a hollow outer needle, an outer needle hub secured to the basal end of the outer needle, an inner needle that is to be passed through the outer needle and which has a sharp tip point, and an inner needle hub secured to the basal end of the inner needle.
To pierce the self-retaining needle into a blood vessel of the patient, the inner needle is passed through the outer needle and pierced into the vessel as it projects from the tip of the outer needle. When the tip point of the inner needle gets into the blood vessel, the blood flows in through the opening in the tip and passes through the bore of the inner needle until it fills the interior of the transparent inner needle hub. This phenomenon is commonly called "flashback" and is a sign of the inner needle having secured the blood vessel. After the occurrence of "flashback", both the inner and outer needles are moved forward by a small distance until the tip of the outer needle enters the blood vessel. Then, with the outer needle being held between the finger and thumb, the inner needle is slipped out of the outer needle and the connector of a transfusion line is plugged to the outer needle hub.
The removal of the inner needle and connecting the transfusion line to the outer needle hub must be carried out as quickly as possible. If not, the blood flows back through the outer needle under the blood pressure and leaks out of the opening at the basal end of the outer needle hub to foul the surrounding area.
With a view to solving this problem, it was proposed that an elastic plug through which the inner needle could be pierced should be provided within the outer needle hub so that the liquid-tightness of the plug would prevent the blood from leaking out. An elastic plug assembly based on this idea is described in Unexamined Published Japanese Patent Application (kokai) No. 229133/1996.
The elastic plug assembly however has one major drawback. Before it is used, the inner needle remains pierced through the elastic plug but the portion of the plug which is in contact with the surface of the inner needle deteriorates over time and loses elasticity. If this occurs, the hole remaining after removing the inner needle is not fully closed and the blood may potentially leak out.
To deal with this problem, materials that will not deteriorate over time must be selected and used to make an effective elastic plug. However, the approach of preventing the time-dependent deterioration by selecting appropriate materials has inherent limits. In addition, desirable materials are very expensive and increase the production cost.